My experience of injecting is with insulin, not Trulicity.
However, I frequently find I bruise. I was told this was not a problem - it was just that I had hit a blood vessel.
Like you, it rarely hurt.
The only advice I was ever given was to make sure I used a fresh needle each time as a blunt needle was more likely to cause bruising.
I was also told "Oh well, some people are more prone to bruising that others." So over time, I just accepted it ... and avoided wearing bikinis ... because no one wants to see my bright white flesh, let alone my bright white flesh with bruises.
Maybe someone else may come along with experience of Truliciy and more helpful advice from HCP.
But, if it was me and it didn't hurt, I wouldn't worry ... just bring it up at my next appointment.